The easiest and most difficult species of plains game

Out of all of the species of plains game you have hunted, what would you say was the easiest? What was the most difficult. I'd be very interested to see if people could put them in some kind of order such as :-

Let's not forget Zebra, bump one of those guys and they will be running till the morning.
Black wildebeast, if you get them to stop all that damn running around.
Kudu, damn things just vanish in the bush.
easist would be warthog, bump one of them just freeze and a few minutes later they will come right back to check out if your gone yet.

I think this is very difficult to answer.
Maybe specify a little more - which is the easiest to get a shot opportunity on or so. One of my mosy difficult hunts was an impala, but also one of my easiest was impala... They know when they being hunted I believe... The ostrich I'm still trying to shoot (with bow) will definitely rank high up on that list when I get him.
If we talking tough - to me the black wildebeest was the toughest - but then again some will say blue, others will say warthog when talking pound for pound.

I dont think there is an "easy" animal to hunt anywhere, but there definitely are difficult ones! Some will be tough and can take a heavy knock from a bullet/arrow and still run a good 150 metres, others will just "vanish" when they were there a second ago, and then some just have to many eyes and ears on the lookout to bust you when you trying to get a shot.

Still looking for eland bull.
Sitatunga was challenging but got one!
Sable came easy.
Took 3 tries to get a kudu over 50.
Both buff were realtively easy.
Botswana lechwe was easy.
Lion was tough hunting, didnt get one.
Its why its called hunting.